The effects of various pretraining procedures and the relationship between speed of acquisition and relative temporal proximity to reinforcement are analyzed in terms of potential roles of contextual stimuli in conditioning. An inverse relation between speed of acquisition and the value of contextual stimuli is suggested and analyzed from the theoretical points of view of both the Rescorla-Wagner model and an application of Gibbon's scalar expectancy theory to acquisition. This proposal requests funds for autoshaping experiments analyzing the effects of the number of US-only presentations and the duration interreinforcement interval on contextual values. Both direct measures of behavior controlled by background cues and transfer tests are proposed as measures of context value.